The present invention relates generally to data verification applications, and more specifically, to the dynamic reconstruction of a signature generated on a digitizer tablet.
The process of visually comparing signatures to check for forgeries is well-established. For example, banks have signature cards for their customers on file, and tellers can compare the signature on a check or other document with the signature card if there is any question as to the authenticity of the signature. In other instances it may be necessary to compare electronically generated signatures. This form of signature can be authenticated using either an automated, computer based verification system or by relying on human examiners.
In general, signature verification techniques rely on the static or "as written" image of the signature. Unfortunately, reliance on this form of the signature only provides a modicum of security since a skilled forger can often duplicate a static signature with sufficient accuracy to circumvent detection. Furthermore, it is normally quite easy to obtain static images of a person's signature, thus providing the would-be forger with all of the necessary information.
Digitizer tablets are known for data input applications. Typically, digitizer tablets are used for capturing primarily spatial and sequential information. When something is written on a digitizer tablet, the output is a parametric representation of the writing trajectory; that is, the writing is represented as a series of x, y coordinate values as a function of time. A typical digitizer tablet samples the position of the writing pen 100 times per second, at fixed intervals of 0.01 seconds. The tablet continuously transmits the resulting data to the receiving computer. Thus every 0.01 seconds, the tablet samples the pen position and transmits an x-coordinate value, a y-coordinate value, and an additional value which indicates whether the pen is up or down. Since the sampling occurs at uniform time intervals, the physical or spatial distance the pen travels between samples is proportionally larger where the writing is fast and proportionally smaller where the writing is slow. The velocity of writing is proportional to the distance travelled between sampled points. This feature may be applied to other data gathering functions.
What is needed is a method of dynamically reconstructing handwritten information, thereby providing a highly reliable technique for detecting a forgery.